How many times we can submit our url in the directories and search engines?

Generally submitting it once is enough, its a bit of a common misconception that frequent submissions will get you a good listing, more likely than not too many frequent submission could get you banned for spamming the search engine. For example Google suggest a link, will tell you that once you've submitted it will be added to the index to have the search engine crawl the site. The tricks with submission are.. Submit manually, don't really on the autosubmitters. -Submit only to the top 5 or search engines (google, yahoo, msn, ask, iwin ), they garner about 95% of the search traffic - Focus on getting as many sites to link to you as possible, this is the most valuable criteria today for search engine placement. good luck